With increases in capacity of information processing in recent years, various information recording techniques have been developed. Particularly, the areal density of HDD using the magnetic recording technique has continued to increase at an annual rate of almost 100%. Recently, it has been required that 2.5-inch magnetic disks used in the HDD or the like have the information storage capacity exceeding 160 GB per disk, and to respond to such requirements, it is desired to actualize the information recording density exceeding 250 gigabits per square inch.
To achieve the high recording density in magnetic disks used in the HDD, etc. in recent years, perpendicular magnetic recording system magnetic disks (perpendicular magnetic recording disks) have been proposed. In the conventional longitudinal magnetic recording system, easy axis of the magnetic recording layer is oriented in the plane direction of the substrate surface. Meanwhile, in the perpendicular magnetic recording system, easy magnetization axis is adjusted to be oriented in the perpendicular direction to the substrate surface. In the perpendicular magnetic recording system, as compared with the longitudinal recording system, the demagnetizing field (Hd) reduce and the coercive force Hc becomes higher as magnetic grains are finer, and it is thereby possible to suppress the phenomenon of heat fluctuation. The perpendicular magnetic recording system is thus suitable for increasing the recording density.
Further, with such increases in the information recording density, both densities continue to increase i.e. the linear recording density (BPI: Bit Per Inch) in the circumferential direction of the magnetic disk, and the track density (TPI: Track Per Inch) in the radius direction. Further, techniques have been studied to narrow spacings (magnetic spacings) between the magnetic layer of the magnetic disk and Read/Write elements of the magnetic head so as to improve the S/N ratio. The flying height of the magnetic head is 10 nm or less that has been desired in recent years.
With decreases in the flying height of the magnetic head as described above, the possibility has increased that the magnetic head contacts the disk surface by external impact and/or fluctuations in flying. Therefore, the perpendicular magnetic recording disk is provided with a medium protective layer to protect the surface of the magnetic recording layer against being scratched when the magnetic head collides with the perpendicular magnetic recording disk. The medium protective layer is formed of a carbon over coat (COO) i.e. a coat with high hardness by carbon coat. In some medium protective layer coexist hard diamond-like bonding of carbon and soft graphite bonding (for example, Patent Document 1). Meanwhile, another technique is disclosed that a diamond-like bonding protective layer is manufactured by a CVD (Chemical Vapour Deposition) method (for example, Patent Document 2).
Further, to protect the medium protective layer and the magnetic head when the magnetic head collides, a lubrication layer is formed on the medium protective layer. For example, the lubrication layer is formed by applying perfluoropolyether and sintering.    Patent Document 1: Japanese Laid-Open Patent Publication No. H10-11734    Patent Document 2: Japanese Laid-Open Patent Publication No. 2006-114182